% Minimize the problems of bad catcodes by doing all the \let's at the end!
\begingroup
  \catcode`b\active % boulder
  \gletb\seeBoulder
  \catcode`h\active % crater
  \gleth\seeHome
  \catcode`m\active % martian
  \gletm\seeMartian
  \catcode`c\active % crater
  \gletc\seeCrater
\endgroup
\begingroup
  \let\gl\glet\catcode`t\active
  \global\deft{\pulse}     % hack: add a clock!
\endgroup

\begingroup
  \catcode`I\active % init
  \global\letI\init
  \catcode`B\active % hit boulder
  \global\letB\boulderHit
  \catcode`C\active % hit crater
  \global\letC\craterHit
  \catcode`K\active % killed
  \global\letK\martianHit
  \catcode`S\active % success!
  \global\letS\success
  \catcode`E\active % end
  \global\letE\endTrial
  \catcode`T\active % telemetry
  \global\letT\telem
\endgroup

\def\activecodes{
  \catcode`I\active\catcode`B\active\catcode`C\active\catcode`K\active
  \catcode`S\active\catcode`E\active\catcode`T\active\catcode`b\active
  \catcode`h\active\catcode`m\active\catcode`c\active\catcode`t\active
}